The invention relates to coal-burning utility electrical power generation plants, and more particularly to a mill head trunnion seal spacer.
In a coal-burning utility electrical power generation plant, a ball tube mill is provided for pulverizing the coal. The mill includes a drum rotational about an axis and having mill heads at distally opposite axial ends thereof The mill heads have mill head extensions extending axially. Stationary cylindrical seal rings and seal sleeves are concentric with the mill head extensions and define an air gap therebetween. The rings have air fittings for introducing air to the mill head to create a pressure differential at the area of the seal, to prevent coal dust from entering such area. Each axial end mill head has a seal cage with a pair of spaced annular seals between the respective mill head extension and ring, and sealing the annular gap therebetween to prevent leakage of coal dust through such annular gap. A spacer is provided between the seals to maintain the seals in axially spaced relation.
In the prior art, problems have been experienced with leakage of coal dust past the seals. In accordance with the present invention, it is believed that such leakage is due to rolling movement of the seals within the seal cage, permitting bypass of coal dust. The rolling movement of the annular seals is transverse to the direction of rotation of the mill head and parallel to the axis of such rotation. In accordance with this belief and recognition, the present invention addresses the coal dust leakage problem by modifying the spacer to prevent the noted rolling or other creeping of the seals between the spacer and the mill head extension and between the spacer and the ring. The spacer of the present invention has been found particularly effective, and has substantially reduced the noted coal dust leakage problem, including over longer life spans than in the prior art.